Well I removed the shift position switch, and it appears to be pretty damaged. See below pics before and after dismantling. I assume this part will be either expensive or impossible to replace without ordering from Japan, so I might just start stripping the car without knowing if the motor etc will run.

We repaired the sensor switch, and now it's back on and the correct gear is shown on the dash when moving through the gears. Unfortunately I still can't get it to run as some other error is preventing operation. There is a constant alert sound that starts a little while after turning the ignition and doesn't stop until turning off. By the way the back wheel is still off and the car is on stands at the back.